I do that.
I first click the eye dropper tool next to Select Effect Range.
Then, in the Video Preview window, I select the color that I want. (I actually drag the dropper to select variations of that color.)
Then, I click the checkbox next to Show Mask.
The Video Preview window simply turns white.
I adjust the sliders under the Limit Luminance, Limit Saturation, and Limit Hue options. Nothing.